Soft ordered mesoporous materials from nonionic isoprenoid-type monoethanolamide amphiphiles self-assembled in water

Abstract

The thermal and lyotropic liquid crystalline phase behaviour of a series of amide and monoethanolamide amphiphiles with isoprenoid-type hydrocarbon chains has been investigated. The amphiphilic nature of these molecules combined with their ability to form nanostructured self-assemblies makes them ideal candidates as delivery vehicles of bioactive molecules. For both families of molecules, increased branching in the hydrophobic chain, associated with increasing chain length, results in a decreased melting point. The melting points of the amides are significantly higher than their monoethanolamide homologues. Interestingly, both hexahydrofarnesoyl (H-farnesoyl) and phytanoyl monoethanolamide exhibit a glass transition temperature at around −72 °C to −74 °C. H-Farnesoyl and phytanoyl monoethanolamide form lyotropic liquid crystalline phases in water, whilst H-farnesoyl and phytanoyl amide form a spontaneous emulsion at the amphiphile–water interface. In particular, at room temperature H-farnesoyl and phytanoyl monoethanolamide form the Schwarz diamond (Q_II^D) and the Schoen gyroid (Q_II^G) bicontinuous cubic phases which are retained down to temperatures as low as 1 °C. Furthermore, phytanoyl monoethanolamide displays a Q_II^D, Q_II^G and inverse hexagonal phase (H_II) at physiological temperature. Both phytanoyl and H-farnesoyl monoethanolamide form mesoporous cubic phases at room temperature that are easily dispersed into cubosomes. The robust nature of the nanostructured phase formation of these two monoethanolamides over a wide range of temperatures makes them ideal candidates for a variety of applications.